Add addStreams to RTCRtpSender

Author: amantoux

lib/src/rtc_rtp_sender.dart

@@ -1,5 +1,6 @@
 import 'dart:async';
 
+import 'media_stream.dart';
 import 'media_stream_track.dart';
 import 'rtc_dtmf_sender.dart';
 import 'rtc_rtp_parameters.dart';
@@ -16,6 +17,8 @@ abstract class RTCRtpSender {
 
   Future<List<StatsReport>> getStats();
 
+  Future<void> setStreams(List<MediaStream> streams);
+
   RTCRtpParameters get parameters;
 
   MediaStreamTrack? get track;